Apparatus and methods for chemical electrodeposition on a substrate for solar cell fabrication

ABSTRACT

The invention relates generally to electrodeposition apparatus and methods. The invention finds particular use in fabricating thin film solar cells. Electrodeposition is improved by using a continuous thin film flow of electrodeposition solution between a substrate and a counter electrode, positioned in close proximity to each other, while the plating current is applied. Apparatus for carrying out methods described herein are highlighted particularly by flow manifolds that allow electrodeposition in the manner described.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of priority under 35 U.S.C. §119 toU.S. Provisional Application Ser. No. 61/169,211, filed Apr. 14, 2009,and to U.S. Provisional Application Ser. No. 61/171,007, filed Apr. 20,2009, both of which are incorporated by reference herein for allpurposes.

FIELD OF INVENTION

This invention relates generally to electrodeposition apparatus andmethods. Methods and apparatus of the invention find particular use insolar cell fabrication.

BACKGROUND

Electrodeposition is a plating process that uses electrical current toreduce or oxidize chemical species of a desired material from a solutionand coat a conductive substrate with a thin layer of that material. Anelectroplating apparatus typically includes two electrodes, a substrateserving as one electrode and a counter electrode. Additionally, areference electrode may also be employed. In an electrodepositionprocess, typically the part to be coated is one of the electrodes andthe coating material is supplied from the electrolyte in which theelectrodes are immersed. In electroplating, the electrolyte isreplenished periodically with the chemical species being deposited onthe substrate. Sometimes, the electrode that is not being coated can bea source of the chemical species in order to replenish the electrolyticsolution.

Solar or photovoltaic cells are devices that convert photons intoelectricity by the photovoltaic effect. Solar cells are assembledtogether to make solar panels, solar modules, or photovoltaic arrays.Solar cells are stacked structures, having layers of materials,including photovoltaic materials, stacked on a substrate for support ofthe stack. There are many fabrication techniques used fabricating theindividual layers of the stack. One particularly useful method iselectrodeposition, however there are drawbacks to conventional apparatusand methods in this respect.

What is needed, therefore, are improved apparatus and methods forelectrodeposition. Given the demand for renewable energy, improvedapparatus and methods are particularly important for solar cellfabrication.

SUMMARY

The invention relates generally to electrodeposition apparatus andmethods. The invention finds particular use in fabricating thin filmsolar cells. The inventors have found that electrodeposition can beimproved in many ways by using a substantially continuous flow, forexample laminar or turbulent, of electrodeposition solution between asubstrate and a counter electrode, where the substrate and the counterelectrode are positioned in close proximity, for example on the order ofmillimeters or less, to each other while the plating current is applied.Apparatus for carrying out methods of the invention are highlightedparticularly by novel flow manifolds that allow electrodeposition in themanner described.

One embodiment is an electrodeposition apparatus for fabricating aphotovoltaic cell, including: (i) a movement assembly for positioning asubstrate in close proximity, for example on the order of millimeters orless, to a counter electrode during electrodeposition; and (ii) a flowmanifold configured to flow an electrolyte between the substrate and acounter electrode and continuously supply electrolyte between theplating surface of the substrate and the counter electrode; where thecounter electrode is positioned on, or an integral component of, theflow manifold. Apparatus described herein find particular use whenemploying a substrate that is a continuous sheet type substrate so thatimproved mass production of thin films is realized. Several flowmanifold embodiments are described in more detail below.

Another embodiment is an electrodeposition method including: (i) flowingan electrolyte between a substrate and a counter electrode using a flowmanifold that supplies a substantially continuous supply of electrolyteto the substrate while the plating surface of said substrate is in closeproximity, for example on the order of millimeters or less, to thecounter electrode; and (ii) applying a plating potential between thesubstrate and the counter electrode; where the counter electrode isconfigured to substantially span at least one dimension of the substrateand is positioned on, or an integral component of, the flow manifold.Particular aspects of methods of the invention are described below.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 depicts a cross-sectional view of a solar cell photovoltaic stackstructure.

FIG. 2 depicts a conventional photovoltaic stack formation scenario.

FIG. 3 depicts a conventional electrodeposition apparatus for solar cellfabrication.

FIG. 4 depicts a perspective view of a flow manifold in accord withembodiments of the invention.

FIGS. 5A and 5B depict a cross-sectional side and front view,respectively, of an electrodeposition apparatus in accord withembodiments of the invention.

FIG. 6 depicts a perspective view of another flow manifold in accordwith embodiments of the invention.

FIG. 7 depicts a perspective view of another flow manifold in accordwith embodiments of the invention.

FIG. 8A depicts an exploded view of an electrodeposition apparatus inaccord with embodiments of the invention.

FIG. 8B depicts a side cross-section view of the electrodepositionapparatus in FIG. 8A.

FIG. 9 depicts a side cross-section view of another electrodepositionapparatus in accord with embodiments of the invention.

FIG. 10 depicts a perspective view of another flow manifold in accordwith embodiments of the invention.

FIG. 11 depicts a cross sectional view of an electrodeposition systemwhich includes more than one electrodeposition apparatus in accord withembodiments of the invention.

FIG. 12 depicts a process flow for an electrodeposition method in accordwith embodiments of the invention.

DETAILED DESCRIPTION A. Making a Solar Cell

FIG. 1 depicts a simplified diagrammatic cross-sectional view of atypical thin film solar cell, 100. As illustrated, thin film solar cellstypically include the following components: back encapsulation, 105,substrate, 110, a back contact layer, 115, an absorber layer, 120, awindow layer, 125, a top contact layer, 130, and top encapsulationlayer, 135.

Back encapsulation can generally serve to provide encapsulation for thecell and provide mechanical support. Back encapsulation can be made ofmany different materials that provide sufficient sealing, moistureprotection, adequate mechanical support, ease of fabrication, handlingand the like. In many thin film solar cell implementations, backencapsulation is formed from glass although other suitable materials maybe used.

A substrate layer can also be used to provide mechanical support for thefabrication of the solar cell. The substrate can also provide electricalconnectivity. In many thin film solar cells, the substrate and backencapsulation are the same. Glass plate is commonly used in suchinstances. Where electrical connectivity is also desired, glass coatedwith a transparent conductive coating can be used.

A back contact layer can be formed from a thin film of material thatprovides one of the contacts to the solar cell. Typically, the materialfor the back contact layer is chosen such that the contact resistancefor the electrons/holes flowing from/to the absorber layer is minimized.This result can be achieved by fabricating an ohmic or a tunneling backcontact layer. This back contact layer can be formed from many differentmaterials depending of the type of thin film solar cell. For example, incopper indium gallium diselenide (CIGS) solar cells, this layer can bemolybdenum. In cadmium telluride (CdTe) thin film solar cells, this backcontact layer can be made, for example, of nickel or copper. Thesematerials are merely illustrative examples. That is, the materialcomposition of the back contact layer is dependent on the type ofabsorber material used in the cell. The thickness of a back contactlayer film is typically in the range of a few microns.

The absorber layer is a thin film material that generally absorbs theincident photons (indicated in FIG. 1 by the squiggly arrow lines) andconverts them to electrons. This absorber material is typicallysemiconducting and can be a p-type or an n-type semiconductor. Anabsorber layer can be formed from, for example, CIGS, CdTe or amorphoussilicon. The thickness of the absorber layer depends on thesemiconducting material, and is typically of the order of microns,varying from a few microns to tens of microns.

A window layer is also typically a thin film of semiconducting materialthat creates a p-n junction with the absorber layers and, in addition,allows the maximum number of photons in the energy regime of interest topass through to the absorber layer. The window layer can be an n orp-type semiconductor, depending on the material used for the absorberlayer. For example, the window layer can be formed from a cadmiumsulphide (CdS) n-type semiconductor for CdTe and CIGS thin film solarcells. The typical thickness of this layer is of the order of microns.

A top contact is typically a thin film of material that provides one ofthe contacts to the solar cell. The top contact is made of a materialthat is transparent to the photons in the energy regime of interest forthe solar cell. This top contact layer is typically a transparentconducting oxide (TCO). For CdTe, CIGS, and amorphous silicon thin filmsolar cells, the top contact can be formed from, for example, indium tinoxide (ITO) or doped zinc oxide (ZnO). The top contact layer thicknesscan be of the order of tens of microns.

A top encapsulation layer can be used to provide environmentalprotection and mechanical support to the cell. The top encapsulation isformed from a material that is highly transparent in the photon energyregime of interest. This top encapsulation layer can be formed from, forexample, glass.

Thin film solar cells are typically connected in series, in parallel, orboth, depending on the needs of the end user, to fabricate a solarmodule or panel. The solar cells are connected to achieve the desiredvoltage and current characteristics for the panel. The number of cellsconnected together to fabricate the panel depends on the open circuitvoltage, short circuit current of the cells, and on the desired voltageand current output of the panel. The interconnect scheme can beimplemented, for example, by laser scribing for isolation and/orinterconnection during the process of the cell fabrication. Once thesepanels are made, additional components such as bi-pass diodes,rectifiers, connectors, cables, support structures etc. are attached tothe panels to install them in the field to generate electricity.Installations can be, for example, in households, large commercialbuilding installations, large utility scale solar electricity generationfarms and in space, for example, to power satellites and space craft.

As mentioned above, electrodeposition is an attractive methodology fordepositing various layers of thin film solar cells. Processes have beendeveloped for the deposition of the back contact, absorber, window andtop contact layers using electrodeposition.

Solar cell photovoltaic stacks are conventionally constructed in anorder starting from, for example, a top encapsulation layer, a topcontact layer, a window layer, an absorber layer, a back contact layerand so on, that is, in an order opposite of the description of thelayers with reference to FIG. 1.

FIG. 2 shows a diagrammatic illustration of conventional photovoltaicstack formation. For illustration purposes, FIG. 2 is described in termsof CdTe-based solar cells. The process starts with the top encapsulationlayer, and the cell stack is built by subsequent depositions of topcontact layer, window layer, absorber layer, etc. The order offabrication is indicated by the heavy arrow in FIG. 2. Other layers maybe formed in addition to the described layers and formation of some ofthe described layers is optional, depending on the desired cell stackstructure.

Referring again to FIG. 2, the TCO-coated glass (for example, the topencapsulation layer 205 and top contact layer 210) can be initiallycleaned, dried, cut to size, and edge seamed. Float glass withtransparent conductive oxide coatings, for example indium tin oxide,fluorinated tin oxide and doped zinc oxide, are commercially availablefrom a variety of venders, for example, glasses sold under the trademarkTEC Glass™ by Pilkington of Toledo, Ohio, and SUNGATET™ 300 andSUNGATET™ 500 by PPG Industries of Pittsburgh, Pa. TEC Glass™ is a glasscoated with a fluorinated tin oxide conductive layer. A wide variety ofsolvents, for example deionized water, alcohols, detergents and thelike, can be used for cleaning the glass. As well there are manycommercially available industrial-scale glass washing apparatusappropriate for cleaning large substrates, for example, Lisec™ (a tradename for a glass washing apparatus and process available from (LISECMaschinenbau Gmbh of Seitenstetten, Austria).

Once the ITO coated glass is cleaned, a CdS layer, 215, may then bedeposited, for example, by using an aqueous solution of, for example, acadmium salt and elemental sulfur composition. The solution does nothave to be aqueous. That is, other solvents, such as dimethylsulfoxide(DMSO), can be used. This deposition can be done usingelectrodeposition. For electrodeposition, the ITO coated glass can formone of the electrodes. The other electrode can be, for example, made ofgraphite, and the electrolyte can be, for example, a DMSO solution of acadmium salt and elemental sulfur. Potential is applied between theelectrodes so that CdS is deposited from the solution onto the ITOcoated glass substrate. Another method of depositing the CdS layer ischemical deposition, for example via wet chemistry or dry applicationsuch as CVD. The CdS deposited is an n-type semiconductor and itsthickness is typically between 500 Å and 1 μm. Subsequent to thedeposition, the layer can then be annealed, for example under an inertatmosphere such as argon, to achieve film densification and grain growthto improve the electrical and mechanical properties of the CdS film.

A cadmium telluride layer, 220, can then be electrochemically depositedon the CdS/TCO/Glass stack (now a substrate for electrodeposition), forexample, from an acidic or basic media containing a cadmium salt andtellurium oxide. In this process, the CdS/TCO/Glass substrate forms oneof the electrodes and platinum or other materials can be used as theother electrode. The electrolyte can contain an acidic or basic media,in solvents such as water, DMSO or other solvents, with a cadmium saltand tellurium oxide, for example. Films of thickness ranging from 1 to10 μm are typically deposited. Cadmium telluride films may then beannealed at approximately 500° C. in an air or oxygen or CdCl₂environment so as to improve the electrical properties of the film andalso to convert the CdTe film to a p-type semiconductor. It is believedthat these methods optimize grain size and thus improve the electricalproperties of the films.

After this CdTe deposition and annealing, a laser scribing process istypically performed to remove CdS and CdTe from specific regions (notshown). In this scribing operation, the laser scribing is utilized suchthat CdS and CdTe are ablated from specific regions of the solar panel.However, the conductive oxide (e.g., Al doped ZnO or ITO) is not removedby the laser scribe.

A back contact layer, 225, can then be deposited on the CdTe layer,using for example sputtering or electrodeposition. For example, copper,nickel and/or other metals, alloys and composites can be used for theback contact layer. This back contact fabrication step can be followedby an anneal, for example, at temperatures of between about 150° andabout 200° C. to form an ohmic contact. The back contact layer can coverthe CdTe layer and also fill the vias (not shown) created in theCdTe/CdS layer by the laser scribing process.

After back contact layer deposition and annealing, laser scribing cantypically be used to remove back contact layer material from specificareas, but the CdTe layer is not etched away in this process. Thisremoval step can complete the process for isolation and interconnectingthe solar cells in series in the solar panel/module.

After the deposition of the back contact layer, an encapsulation layer,230, can be applied, for example, using ethylvinyl acetate (EVA).Encapsulation protects the photovoltaic stack. Glass, 235, can be addedfor further structural support (and protection) of the stack.

The above described fabrication process represents a brief outline andmany variants of this process can be employed for the fabrication ofCdTe thin film solar cells. For other types of thin film solar cells,different chemicals, etc. can be employed. In this description, exampleprocess steps have been described for illustrative purposes. Other stepswould typically include additional details of the laser scribing andablation steps employed for the fabrication of the interconnect schemesand cell isolations, multiple clean and drying steps between thedifferent layer depositions and the like. Values for the layerthicknesses, anneal temperatures, chemical composition etc. describedare merely illustrative. These values can vary across a wide range asprocesses are optimized for many different output variables.

FIG. 3 is a simplified cross-sectional illustration of a conventionalelectrodeposition apparatus, 300, that employs a continuous substrate.So as not to complicate the description, other components of theequipment, such as the electronics for control systems, for applyingpotentials to the electrodes, chemical handling system for theelectrolyte etc., are not shown, but would typically be included in thesystem. The dimensions of the different components of the system canvary across a large range depending on the application for which theequipment is designed. FIG. 3 is a schematic of equipment that is usedin conventional electrodeposition of various layers for solar cellfabrication on a continuous substrate. As shown, apparatus 300 includesa large tub, 305, which holds the electroplating solution, 310, andthrough which a continuous substrate, 315 is passed. Deposition on thesubstrate is achieved by application of an electric potential betweenthe substrate, for example a metal foil, and a counter electrode, 320. Alarge tub typically contains the electroplating solution, counterelectrode 320, and a mechanism, for example rollers, 325, for moving thesubstrate through the electroplating zone etc. The moving foil is thesubstrate on which deposition takes place. This foil also forms one ofthe electrodes of the electrodeposition system. The foil electrode canbe made of a wide variety of materials, but generally will beelectrically conductive, chemically compatible with the electrolyticsolution. For example, the foil or substrate can be made of aluminum,nickel, steel and the like.

The counter electrode is the second electrode in the system and istypically immersed in the electrolytic solution. This counter electrodecan be made of a large variety of materials. Typically, the counterelectrode is electrically conductive and chemically compatible with theelectrolytic solution. For example, the counter electrode may be formedfrom materials, such as platinum and/or graphite.

Conventional electrodeposition apparatus that employ a continuoussubstrate will typically include a mechanism for moving the substratethrough the active electroplating zone. This movement mechanism may bein the form of rollers, 325. These rollers are used to move thesubstrate through the system and the electrolyte and over the counterelectrode to enable electrodeposition. Substrate 315 is curled (or bent)as it passes over each roller, in this example the foil substrate isbent four times as it passes into and out of the electrolyte bath and onto further processing steps. If any of these rollers are immersed in theelectrolyte or are in contact with it, care is typically taken to ensurethat the roller material of construction is chemically compatible withthe electroplating solution.

The composition of the electrolyte depends on the material to bedeposited. Examples of electroplating solutions that might be used forfabricating different layers of the CdTe solar cell are described abovein relation to FIGS. 1 and 2.

Conventional apparatus, such as that described in relation to FIG. 3,can suffer from some significant drawbacks. One drawback is maintenance,for example, conventional electrodeposition equipment requires immersionof moving parts of the equipment in the electroplating solution.Electroplating solutions can have harsh, caustic chemicals, which causedegradation of these parts and create maintenance challenges. Theseimmersed parts also have to be fabricated using materials that arecompatible with these harsh chemicals, which can raise the cost of theequipment significantly.

Another drawback of conventional electrodeposition apparatus is relatedto chemical consumption. In a typical implementation ofelectrodeposition equipment the chemical consumption can be very high.First, the chemical is held in a large bath, and it is challenging toreplenish the chemical in-situ to maintain the chemical concentrationsof the depositing species. Second, chemical deposition in thisconfiguration can also occur on the wall of the tub and on the immersedparts of the equipment. This non-specific or extraneous depositionincreases the chemical consumption and also increases the cost andcomplexity of maintenance. Third, in conventional bath-type systems itis difficult to prevent deposition on both sides of the continuoussubstrate, which is undesirable in many applications and uses excesselectrolytic solutions. Finally, use of large quantities of potentiallytoxic chemicals can also present an increased safety hazard and increasethe cost of running the equipment to appropriately mitigate this risk.

Another drawback of conventional electrodeposition apparatus is relatedto deposition uniformity. Achieving deposition uniformity in thisconfiguration poses significant challenges, for example, achieving asubstantially parallel plate configuration is difficult in conventionalapparatus. This can create edge effects and lead to non-uniformdeposition. It is also difficult to maintain uniform substrate andsolution temperature, and uniform substrate potential, furthernegatively impacting the deposition uniformity. It is also challengingto provide uniform solution agitation, while maintaining a flatsubstrate, since the foil is flexible.

Yet another drawback of conventional electrodeposition apparatus isrelated to modularity and interchangeability. In the conventionalimplementation of the equipment, it is challenging to use the sameequipment for different processes. To be able to use the equipment fordifferent processes, the materials compatibility of the immersed partsto the different chemicals has to be evaluated for each application.Different processes have different deposition rates and layer thicknessrequirements, which require flexibility in the variables used to achievethese outcomes, for example, the length of the electrodes and/or therate at which the substrate is moving.

With conventional apparatus, it is not readily feasible to change therate of the motion if the process consists of multiple depositions. Inconventional implementations, it is challenging to change the length ofthe electrode since that would require changing the size of the bathetc. or significantly underutilizing the bath and the chemical bydesigning the bath for the longest deposition in the process flow. Also,by requiring that the substrate be directed into, and out of, a bath viaa system of rollers, the substrate and its newly deposited film aresubjected to bending over at least two rollers, four rollers in theexample depicted in FIG. 3. If multiple layers were deposited using oneor more conventional electrodeposition baths and a continuous substrate,the photovoltaic stack formed on the substrate is subjected to multiplebends over many rollers which can negatively affect the ultimateperformance of the stack.

B. Apparatus and Methods

For illustration purposes only, electrodeposition is sometimes describedherein as being used in the fabrication of CdTe-based solar cellsalthough electrodeposition can be used to fabricate any number of othertypes of solar cells or other types of thin films products and/ordevices. That is, the invention is not limited to this exemplaryelectrodeposition chemistry.

The inventors have found that many of the drawbacks of conventionalelectrodeposition apparatus, for example as described in relation toFIG. 3, can be overcome using methods and apparatus in accord withembodiments of the invention. More specifically, and in very generalterms, instead of immersing the substrate in a volume of electrolyte, aflow of electrolyte is applied to a surface of the substrate. Theinventors have found that novel flow manifolds in conjunction withappropriate substrate handling and electrodeposition components, such aspotential source controllers and the like, appropriately configured,allow the substrate and counter electrode to be brought in closeproximity to one another during plating, which provide advantages, forexample, using less electrolyte, obviating the need to bend and directthe substrate into an electrolyte bath, establishing substantiallyparallel plate conditions for highly uniform deposition, and obviatingthe need for moving parts exposed to the bath. Further advantages aredescribed below.

Various implementations of embodiments of the invention are described inmore detail below. These implementations are meant to be illustrative,non-limiting examples. One of ordinary skill in the art would appreciateother variants of the following examples by reading the descriptionherein. Various exemplary electrodeposition apparatus and methods inaccord with embodiments of the invention will first be described andpotential benefits of these implementations will be describedthereafter.

One embodiment is an electrodeposition apparatus for fabricating aphotovoltaic cell, including: (i) a movement assembly for positioning asubstrate in close proximity to a counter electrode duringelectrodeposition; and (ii) a flow manifold configured to flow anelectrolyte between the substrate and a counter electrode andcontinuously supply electrolyte between the plating surface of thesubstrate and the counter electrode; where the counter electrode ispositioned on, or an integral component of, the flow manifold. In oneembodiment, the movement assembly includes a drive component configuredto move the substrate past the flow manifold and counter electrodeduring electrodeposition without substantially bending the substrate. Inone embodiment, the substrate includes a continuous sheet that includesat least one of an electrically conductive material and a materialhaving an electrically conductive coating. Conductive materials include,for example, aluminum, stainless steel, titanium and graphite foil. Amaterial having an electrically conductive coating would be, forexample, a glass, plastic, polymer or other substrate coated with aconductive coating, for example, a conductive oxide such as atransparent conductive oxide, for example, fluorinated tin oxide, indiumtin oxide and the like.

FIG. 4 depicts a perspective of a flow manifold, 400, which is acomponent of an electrodeposition apparatus in accordance with oneimplementation of the present invention. Manifold 400 has a body, 405,and in this example, a counter electrode, 410, that is substantiallyplanar with a top surface that is substantially even with the topsurface of manifold body 405. This is only one implementation of flowmanifolds in accord with embodiments of the invention, that is, thecounter electrode can be positioned on the manifold, or as in this case,integral to or recessed in a surface of the flow manifold body.Referring again to FIG. 4, flow manifold 400 has an electrolyte inlet(or injection port), 415, and a used electrolyte outlet, 420. Althoughdepicted as rectangular in shape, inlet and outlet electrolyte ports arenot limited to any particular geometry. As well, there may be, forexample, a series of inlets and outlets that serve the same purpose as asingle inlet and/or outlet. During electrodeposition, a substrate, inthis example a continuous sheet substrate 425, and counter electrode 410are brought within close proximity (as indicated by the heavydouble-headed vertical arrow) of each other. In one embodiment, thecounter electrode and the substrate plating surface are substantiallyparallel planar. In one embodiment, the counter electrode and thesubstrate are between about 2 mm and about 25 mm apart duringelectrodeposition, in another embodiment between about 2 mm and about 10mm apart during electrodeposition, in yet another embodiment betweenabout 2 mm and about 5 mm apart during electrodeposition. In anotherembodiment the counter electrode and the substrate are between about 1mm and about 5 mm apart during electrodeposition, in another embodimentbetween about 1 mm and about 3 mm apart, in yet another embodimentbetween about 1 mm and 2 mm apart. In another embodiment, the counterelectrode and the substrate are between about 0.1 mm and about 2 mmapart.

Although certain embodiments are described as having a substantiallyparallel planar orientation between substrate and counter electrode, thetwo electrodes can be non-parallel, before and/or during plating.Analogous to, for example, the semiconductor arts, controlling theorientation of a plating substrate with respect to the surface of anelectrolyte during entry into an electrolyte and/or during anelectroplating process can be beneficial. For example, bubbles can beentrapped on the plating underside of a plating substrate upon immersioninto the electrolyte. Bubbles sticking to the surface of a substrateduring plating can produce voids in the deposited film. Bubbles can beso entrapped especially when the substrate is immersed in a horizontalorientation (that is, parallel to a plane defined by the surface of theelectrolyte) along a vertical immersion trajectory. If the substratesurface is introduced into the electrolyte on a trajectory normal to thesurface of the electrolyte, i.e. the substrate is angled before entryinto the electrolyte, then entrapment of bubbles can be avoided or atleast minimized. Thus in one embodiment, apparatus allow for angledimmersion into a continuous flow of electrolyte from the manifold. Inother embodiments, the substrate's orientation can be adjusted activelyduring immersion or during electrodeposition. Active angle adjustmentrefers to changing the angle of the substrate relative to a theoreticalplane of the flowing electrolyte across the surface of the flow manifoldat any time during positioning or electrodeposition. This providesflexibility in various electrodeposition scenarios. In a typical, butnon-limiting, example, however, laminar electrolyte flow (as describedin more detail below) is employed which aids in removing any bubblesthat could cause film defects.

Referring again to FIG. 4, substrate 425 and counter electrode 410 arebrought into close proximity of each other, and an electrolyte flow isestablished between them. The direction of the flow in this example isindicated by the dotted arrows, first emanating from inlet 415, and thenexiting into outlet 420. In this example, a continuous flow can beproduced (via appropriate reservoirs and pumps not depicted) that flowsinto the void between the substrate and the counter electrode, betweenthe substrate and the counter electrode, and drains via outlet 420. Inone example, the flow pattern is substantially laminar. The dotted arrowabove substrate 425 indicates the direction of movement of the substraterelative to flow manifold 400. In one embodiment, the continuous sheetsubstrate is moved continuously during electrodeposition, in anotherembodiment the substrate is periodically repositioned in order toelectrodeposit on an area of the substrate that has no film yetdeposited. In other embodiments the electrolyte flow is turbulent.

In certain embodiments, the substrate continuously moves relative to thecounter electrode of the flow manifold. In a specific implementation,the length of the manifold, “L” as depicted in FIG. 4, will depend onthe speed at which the substrate is moving, deposition rate of theelectrodeposition process, and the thickness of the material to bedeposited. The length of the electrode can be given by the formula:

L=T×S/R

where L=length of the electrode, T=thickness of the film to be coated,R=rate of deposition and S=speed of the substrate motion. If, forexample, the thickness of the layer to be deposited is 1 μm, thesubstrate is moving at a speed of 1 foot/minute and the deposition rateof the layer is 1 μm/minute, then the length of the electrode would be:L=(1 μm×1 feet/minute)/(1 μm/minute)=1 foot. In one embodiment, thecounter electrode substantially spans the width of the substrate as thesubstrate passes by the counter electrode during electrodeposition. FIG.4 depicts the counter electrode width as “W.” A single counter electrodeneed not be used, but rather two or more appropriately spaced and/orpatterned counter electrodes can work as well, and are included as analternative embodiment wherever “a counter electrode” is describedherein.

FIGS. 5A and 5B show side and front cross sections, respectively, of anelectrodeposition system, 500, for electroplating on a continuoussubstrate in accordance with a specific implementation of the presentinvention.

Referring to FIG. 5A, apparatus 500 has a flow manifold which includes abody, 505, which has an electrolyte inlet, 515, and outlet, 520. Theflow of electrolyte (540 as indicated in FIG. 5B) duringelectrodeposition is indicated by the dashed arrow going from 515 to520. A substrate, 525, for example a foil, is moved by a roller, 530,which can also provide temperature control and hold the substrate flat,for example, via an applied vacuum to the backside of substrate 525.Roller 530's movement is indicated by curved dashed arrows on roller530, where substrate 525 is delivered to roller 530 from a roll ofsubstrate or the like. Roller 530 can also protect the backside ofsubstrate 525 such that electrodeposited material is applied only to oneside of the substrate. A roller for moving the substrate is typical, butnot necessary. In one embodiment, the roller is replaced, for example,by a skid structure that also may apply potential, provide temperaturecontrol and hold the substrate flat as described in relation to theroller. In the skid embodiment, the substrate is pulled through andbetween the skid and the counter electrode. In a typical process, apotential is applied between substrate 525 and a counter electrode, 510.In this example, counter electrode 510 is recessed into manifold body505 such that the top surface of the counter electrode is flush with thetop surface of the manifold body. The substrate moves over the manifoldthat is used to inject electroplating solution from one end and evacuatesuch solution out the other end of such manifold. The potentialdifference between the substrate and second electrode cause a material,535, from the electrolytic solution to deposit on the surface ofsubstrate 525 opposite that touching roller 530 as substrate 525 movespast, and in close proximity to, the counter electrode. In oneembodiment, the substrate moves continuously, in another embodiment, thesubstrate is moved periodically to electrodeposit while the substrate isnot moving. FIGS. 5A and 5B show one possible implementation of thisequipment. Although one possible implementation is shown, otherimplementations are also possible. For example, the equipment could beinverted so that the manifold is above the moving substrate, or thecomponents could be vertically oriented or at some angle to takeadvantage of gravity, for example, to drive and/or guide electrolyteflow and/or to take into account other fabrication advantages.

One or more potential sources apply a potential difference between thesubstrate (for example, via the movement mechanism) and the electrode sothat a material from the electrolytic solution is deposited on the onesurface of the substrate. The one or more potential source can take anysuitable form such as a direct current source, for example, anadjustable or fixed current source. In this embodiment, the substratecontinuously moves adjacent to the electrode so that a material from thesolution is deposited in a thin film across the entire first surface ofthe substrate.

Manifold body 505 can be constructed from many different materials suchas polytetrafluoroethylene (PTFE, also known as Teflon which isregistered trademark of E.I duPont de Nemours and Company, ofWilmington, Del.), perfluoroalkoxy (PFA), polytetrafluoroethyleneperfluoromethylvinylether (MFA), fluorinated ethylene propylene (FEP),ethylene tetrafluoroethylene (ETFE), ethylene chlorotrifluoroethylene(ECTFE), polyvinylidene fluoride (PVDF), tetrafluoroethylenehexafluoropropylene vinylidene fluoride (THV), polyetheretherketone(PEEK™ is a registered trademark of Victrex of Lancashire, UK),polyetherimide (PEI) and the like. Preferably, these materials arechemically resistant, easy to machine, and electrically insulating.Fluoropolymers are generally well suited for these criteria. Counterelectrode 510 can be made from many different materials. The differentelectrode materials that can be used for fabrication of the differentlayers of the CdTe solar cell, for example, are described above.

Although some embodiments describe the relationship between the counterelectrode and the substrate where the counter electrode substantiallyspans the width of the substrate, any suitable dimensions for thecounter electrode can be used. In one embodiment, the dimensions areselected so that the counter electrode is wider than the substrate beingcoated so that a parallel plate configuration can be maintained and theedge electrical field effects can be minimized. FIG. 5A illustrates acounter electrode wider than the substrate passing over it.

The manifold may optionally include capabilities for pre-clean of thesubstrate and rinsing and drying. For example, a nitrogen, argon and/orair curtain and/or knife can be added at one end of the manifold. In oneimplementation, the gas or gases would be plumbed into the manifold andblown onto the substrate to dry it. Similarly for pre-cleaning andrinsing, de-ionized water or other solvent can be sprayed onto thesubstrate through the manifold. Any one of, and combinations of,pre-cleaning, rinsing, and drying can be done before the substrateenters the electrodeposition zone and after it exits theelectrodeposition zone.

Although a roller provides a movement mechanism for moving thesubstrate/foil, in one implementation of the present invention, othermovement mechanisms may also be utilized. Additionally, but notnecessarily, a heater can be attached to the movement mechanism forheating the substrate. Also, vacuum or suction can be provided to theroller to hold the substrate flat onto the roller. Some other holdingmechanism can also be employed to hold the substrate on the movementmechanism. The roller can also be used for applying potential to thesubstrate. In one embodiment, this potential could be ground withrespect to the counter electrode.

An electrolytic solution can have different compositions, which dependson the process requirements for the layer being deposited. Examples ofelectrolytic solutions that can be employed for depositing differentlayers for the CdTe solar cell are discussed above.

The foil or substrate can take the form of a continuous substrate onwhich the deposition is to be performed and can also act as one of theelectrodes of the system. Different types of foils or substrates can beused. Examples of the different types of electrodes and the requirementsfor the foils are discussed above. The substrate may also take the formof a glass sheet coated with a TCO (which serves as the electrode). Inone embodiment, the substrate is such a glass sheet. In the anotherembodiment, the glass sheet is continuous.

Referring to FIG. 5B, the solution is contained between the substrateand counter electrode 510. Around the perimeter of the gap between thetwo electrodes fluid surface tension can be employed to constrain thesolution, that is, a swell of electrolyte is of sufficient flow, and theelectrodes are close enough together, that fluid surface tension isemployed for containing the solution and no additional sealing isrequired. Additionally, overflow channels, 545, can be constructed tocontain any electrolyte that leaks out (overflow channels are notdepicted in FIG. 5A, but one embodiment includes an overflow channelthat encompasses at least a portion of, optionally all of, the perimeterof the flow manifold).

It is important that the electrolytic solution properly wet the twoelectrodes. One way to achieve this consistently is to apply theelectrolytic solution under sufficient pressure. If the surface tensionis not adequate to contain the solution at a desired injection pressure,seals can be also employed. Thus, one embodiment is the apparatus asdescribed above further including one or more seals, the sealsconfigured to channel the flow of electrolyte in order to maximizecontact with the substrate and minimize the amount of electrolyte neededto produce the continuous supply of electrolyte contacting the substrateduring electrodeposition. For example, one or more seals may be employedto contain the electrolytic solution in the electroplating zone, anddifferent mechanisms can be employed for such containment. Sufficientsealing can be achieved, for example, by using dams, for example madefrom the materials described in relation to manifold 510 or thosedescribed below in relation to sealing elements, around one or moresides of the counter electrode, on or in close proximity to the manifoldbody, to aid in fluid containment. In some embodiments, one or moreseals are attached or in close proximity to at least one of the flowmanifold and the counter electrode. In another embodiment, the one ormore seals are part of a unitary manifold body.

Many different materials could be employed for this containment purpose.In one embodiment, the one or more seals include at least one of PTFE,silicone, butylrubber, and fluoroelastomers such as Viton and Kalrez(Viton and Kalrez are registered trademarks of DuPont PerformanceElastomers, of Wilmington, Del.).

“Seals” for the purposes of certain embodiments need not come in contactwith the substrate. That is, since the counter electrode and thesubstrate are in close proximity to one another, and electrolyte flowand surface tension can be used to compensate for electrolyte lossaround the perimeter of the space between the electrodes, “seals” can beused to aid in containment, while not necessarily completely containingthe electrolyte between the electrodes. Thus, seals can be non-contactand contact-type seals, that is, where the substrate does not touch theseal or the substrate does touch the seal. In one embodiment,non-contact seals are dams, where the substrate comes in closeproximity, for example, on the order of a few millimeters, to amillimeter or less than a millimeter, to the seals but does not touchthem. This close proximity need not entail actual overlap of thesurfaces of the seal and the substrate, that is, the edges of each ofthe seal and the substrate might simply be brought in close proximity inorder to minimize electrolyte loss between them. Also, in the figuresseals are depicted as having a rectangular (or square) cross section. Inother embodiments, invention may not be limited in this way. In oneembodiment, the seals have minimal surface area at the portion of theseal that either contacts or comes in close proximity to the substrate,for example, a “tear drop,” triangular, fin or blade cross section. Whenthe substrate comes in contact with the substrate, the material can bechosen not only to protect the substrate from damage, but also theelectrodeposited material. Certain embodiments include one or morecontact and/or non-contact seals as described in more detail below.

FIG. 6 depicts a flow manifold, 600, which has a body, 605, a counterelectrode, 610, electrolyte inlet and outlets, 615 and 620,respectively, and seals 630 on either side of the counter electrode inaccordance with one embodiment of the present invention. The substrate,625, moves in the direction indicated by the dashed arrow duringelectrodeposition. Although not shown to scale in FIG. 6, typically thesubstrate will span seals 630. If seals 630 are contact seals, then thesubstrate would touch the seals; if non-contact seals, then thesubstrate would come very close, as described above, but not touch theseals. In the event there is overlap of the substrate with the seals,and therefore electrodeposition is blocked, this portion of thesubstrate can be trimmed off at a later stage. As this figure is notdrawn to scale, one of ordinary skill in the art would appreciate thatthe electrodes can be very close to one another and thus seals 630 couldbe quite thin, for example, on the order of less than a millimeter,about a millimeter to a few millimeters thick (in the dimension betweenthe electrodes).

Another embodiment is an apparatus as described above where the one ormore seals are configured to form a flow barrier on each of the sides ofthe substrate parallel to direction of electrolyte flow, and a partialflow barrier on the downstream end of the flow manifold. FIG. 7 depictsa flow manifold, 700, which has a body, 705, a counter electrode, 710,an electrolyte inlet, 715, and a seal, 720, that in this example, spansthree sides of the perimeter of the counter electrode. The substrate,not depicted, moves in the direction indicated by the dashed arrowsduring electrodeposition, that is, parallel to the counter electrode andin a direction from the inlet end of the manifold to the opposite end ofthe manifold. In this example the substrate will span the length andwidth (or close to the width in the case of edge-type non-contactsealing) of seal 720. Seal 720, whether contact-type or not, aids incontainment of the electrolyte in the volume between the electrodes andwithin the three sides of seal 720. Seal 720 can be part of the unitarybody of the manifold, or attached thereto. In this example, apertures725 in seal 720 serves as electrolyte outlets. In one implementation,manifold 700, is part of an electrodeposition apparatus where manifold700 is oriented vertically (or at some angle greater than zero), thatis, where the electrolyte inlet is at the top and apertures 725 are atthe bottom of the manifold so that gravity can be employed to aid inelectrolyte containment (keeping the electrolyte from flowing toward theinlet) and flow (gravity pulling electrolyte down) between theelectrodes. In this configuration, electrolyte would flow in asubstantially laminar fashion between the electrodes as described above.Another embodiment is the apparatus as described in relation to FIG. 7,further including an upstream seal that forms a flow barrier on theupstream end of the flow manifold, where the electrolyte inlet islocated downstream of the upstream seal.

As mentioned above, in some embodiments, there are one or more sealingmembers that aid in containing the electrolyte sufficiently to maintainthe desired flow characteristics during electrodeposition. In someembodiments this arrangement includes sealing, via contact and/ornon-contact seals, a perimeter around the counter electrode. Thus, oneembodiment is an electrodeposition apparatus as described above, whereone or more seals are configured to form a chamber (volume) between thesubstrate and the flow manifold, when the flow manifold and thesubstrate are engaged with, or in close proximity to, the one or moreseals. In one embodiment, the electrolyte inlet and an electrolyteoutlet, are each contained within the chamber during electrodeposition.In one embodiment, the perimeter is established via a single seal, wherethe single is a contact and/or a non-contact type seal. That is, thesingle seal can have portions that contact the substrate and portionsthat do not, depending on the flow and other requirements of the system.The single seal can be, for example, rectangular, oval, round, or anysuitable shape. The single seal can be attached to at least one of theflow manifold and the counter electrode or not attached to either. Inone embodiment, the single seal is configured to be periodically removedbetween plating operations to aid in keeping the chamber clean betweenelectrodepositions. The seal is either cleaned for further use orreplaced with a fresh seal. In one embodiment the single seal isrectangular, for example as depicted in FIG. 8A.

FIG. 8A depicts an exploded view of an exemplary electrodepositionassembly, 800, of the invention. The heavy double headed arrows indicatethat the individual components of the assembly are engaged as indicatedduring electrodeposition. For simplicity, components such ascontrollers, voltage lines, fluid flow lines, pumps, reservoirs, etc.are not depicted. Assembly 800 includes a flow manifold, 805, which hasan electrolyte inlet and outlet as well as a counter electrode asdescribed above in relation to other embodiments. The dashed arrowsindicate the intended flow pattern of electrolyte from the inlet, acrossthe counter electrode and draining via the outlet. Assembly 800 alsoincludes a rectangular seal, 810, a continuous substrate, 815, and aroller, 820. Dashed arrows also indicate intended movement patterns forthe substrate and the roller which engages and moves the substrate.These components can function as described above in relation to otherembodiments, but particulars of this embodiment are described in moredetail below.

FIG. 8B depicts assembly 800 where the components depicted in FIG. 8Aare engaged. Manifold 805 has a body 801 which includes counterelectrode 802 and inlet and outlets, 803 and 804, for the electrolyte toenter and exit the system during electrodeposition. Seal 810, uponengagement with substrate 815 and manifold 805, forms a volume (orchamber) that, in this example, encompasses the perimeter of the counterelectrode and the electrolyte inlet and outlet ports. Thus, once engagedand electrolyte is flowing, a laminar flow of electrolyte is establishedbetween the substrate (electrode) and counter electrode. Again, asmentioned in relation to FIG. 6, the depiction is not to scale, forexample the distance between the electrodes can be quite small andcorrespondingly seal 810 can be less than a millimeter to on the orderof several millimeters thick. Also the cross section of the seal may beother than rectangular, for example, a blade, triangular or teardrop andthe overall shape of the seal can be other than rectangular, forexample, oval, diamond, or other polygon or non-regular shape, dependingupon the desired flow characteristics.

Referring again to the embodiment with respect to FIGS. 8A and 8B, seal810 can be a contact seal, a non-contact seal or a combination of thetwo. In one embodiment, the perimeter seal is a contact seal (sometimesreferred to as a soft seal) as described above, that makes contact withthe substrate around entire perimeter of the seal. In anotherembodiment, the perimeter seal is purely non-contact seal as describedabove, where no actual contact is made with the substrate, but rathercomes close enough that, along with surface tension and flow rate, thereis always electrolyte between the substrate and the counter electrodesufficient for uniform film deposition during electrodeposition. In yetanother embodiment, seal 810 has contact and non-contact components, forexample, where the substrate comes in contact with seal 810 on the sidesparallel to the direction of movement of the substrate, but does notcontact seal 801 at the upstream and downstream sides of seal 810. Inone implementation of this embodiment, the height (or thickness in thedimension measured between the electrodes) of seal 810 is less at theupstream and down stream sides than it is at the sides parallel to thedirection of movement. In another embodiment, the substrate does notcome in contact with seal 810 on the sides parallel to the direction ofmovement of the substrate, but does contact seal 801 at the upstream anddownstream sides of seal 810. In one implementation of this embodiment,the height (or thickness in the dimension measured between theelectrodes) of seal 810 is the substantially uniform, but the substrateonly touches the upstream and downstream sides, for example, because ofthe substrate's limited width as compared to the perimeter seal.

Although seal 810 is depicted as separate from the manifold, it can bepart of the manifold, for example, formed as a feature emanating from aunitary flow manifold body and thus could be thought of as a fluid dam.The flowing electrolyte would flow over the top edge of the dam in theabsence of engagement (contact or not) with the substrate. In the caseof a non-contact seal, the substrate is positioned just above (or nearas where the substrate and seal edges are in close proximity but with nooverlap), for example as little as a few millimeters, a millimeter oreven less than a millimeter away, from the top surface of the dam, sothat only minimal electrolyte escapes from the “chamber” thus formedbetween the electrodes and (within) the dam. Configurations such as thiscan be desirable, for example where minimal electrolyte flows away fromthe substrate, particularly in the regions close to the perimeter of theplating surface where localized eddy currents can interfere with uniformplating. In the event the seals is a contact seal, for example teflon,care has to be taken that the seal does not abrasively damage thesubstrate. Moreover the seals, even if contact type seals, may haveperforations or outlets configured to aid in electrolyte flow patterns,for example, to aid in establishing substantially laminar flow betweenthe electrodes. In one embodiment there are apertures in the perimeterseal, for example as depicted in FIG. 7, where the apertures are locatedon one or more sides, for example the two sides parallel to thedirection of the substrate movement, and/or the downstream end side ofthe seal. These apertures can be used to tailor electrolyte flowpatterns to suit the needs of the user to electrodeposit a particularfilm in a particular way.

Although seal 810 is depicted in FIG. 8B as contacting both thesubstrate and the flow manifold, this is not necessarily the case.“Engagement” for the purposes of this invention includes close proximityengagement without actual contact. Like non-contact sealing as describedabove in relation to the relative positioning of a surface of the sealand the substrate, non-contact sealing can also exist, either alone orin combination with substrate sealing, between a surface of the seal andthe manifold. In one embodiment, the seal 810 is a rigid seal, forexample made of teflon, PEEK, a teflon coated metal (or other supportinfrastructure) member and the like, which is suspended between thesubstrate and the flow manifold during engagement. Since a surface ofthe seal is in close proximity to the manifold, and another surface (orportion, if for example the seal has an oval or circular cross section)of the seal is in close proximity to the substrate, the volume orchamber as described above is formed, even though there is someelectrolyte leaking between the small gap between each of the seal andthe substrate and the seal and the manifold. Such an arrangement cancreate a desirable flow dynamic, for example near the substrate edges asdescribed above, but also at the edges of the counter electrode toenhance uniform plating. Such a configuration can also be beneficial toaid in preventing buildup of materials that would otherwise deposit, forexample, in corners where a seal and the manifold surface meet. Also,such configurations are beneficial because a seal that does not come inphysical contact with the manifold or substrate, in this examplesuspended between the substrate and the manifold, can be easilyinterchanged and cleaned periodically.

Although FIG. 8B depicts the substrate in contact with the seal atsubstantially the same level both at the leading edge of the seal and atthe following edge where the substrate would have a deposited film (notdepicted here) thereon, this arrangement of the sealing surface withrespect to the substrate is not necessary. In one embodiment, the sealsurface at the following edge is lower than that at the leading edge, tocompensate for the thickness of the newly deposited film on thesubstrate that must pass over the following edge of the seal. In oneembodiment this differential height is not necessary because the seal ispliable and does not damage the substrate or deposited film, for examplea soft blade seal, elastomeric and/or spring actuated seal. Asmentioned, one embodiment is a combination of contact and non-contactseals. In one implementation of this combination, the leading edge ofthe seal can be a contact seal while the following edge is a non-contactseal, where the newly deposited film does not make contact with thefollowing edge of the seal. One of ordinary skill in the art wouldappreciate that many combinations are possible without escaping thescope of the invention.

FIG. 8B and FIG. 9 depict electrodeposition assemblies in a verticalorientation. Such an orientation allows gravity to aid in producing alaminar flow (downward) from the inlet side to the outlet side of themanifold. As discussed above, embodiments of the electrodepositionapparatus are not limited to any particular orientation, however.

FIG. 9 depicts a cross sectional view of another electrodepositionassembly, 900, similar to that described in relation to FIGS. 8A and 8B,but with different configuration for the electrolyte inlet and outlet.Assembly 900 includes a manifold with a body, 905, and a counterelectrode, 910. Substrate 920 is driven by roller 930 past the counterelectrode as described above. In this example, seal 915 has one or moreapertures, 930, in its leading side, and one or more apertures, 935, inits downstream side. One or more apertures 930 serve as the electrolyteinlet, and apertures 935 serve as the electrolyte exit from the betweenthe substrate and the counter electrode. The apertures are in fluidcommunication with the appropriate plumbing (not depicted). Thisconfiguration aids in producing a substantially laminar flow byorienting the inlet and outlet flows substantially parallel to theplanes of the substrate and the counter electrode. With respect to thedescription herein that the inlet and outlet are part of the flowmanifold, this is consistent because, for example, seal 915 can be ofthe type that is part of a unitary body of the flow manifold. In otherembodiments, the combination of (or engagement with) a sealing elementand a manifold body are together part of the flow manifold.

As mentioned, neither the seal component, the electrolyte inlet oroutlet, nor the manifold body, of electrodeposition apparatus in accordwith embodiments of the invention are limited to any particulargeometry. In embodiments with a perimeter-type seal, for example, theseal can be rectangular, oval, circular, square, triangular, or anirregular shape and have a cross section that is, for example,rectangular, circular, oval, teardrop, triangular, irregular, i.e. anysuitable shape. Also as mentioned, one aspect of the invention iscreation of substantially laminar electrolyte flow between the substrateand counter electrode during electrodeposition. In apparatus of theinvention, flow characteristics can be achieved, for example, viamanipulation of the configuration of one or more of the seal,electrolyte inlet and outlet, counter electrode, etc. as well as takingadvantage of surface tension, gravity, characteristics of theelectrolyte, for example viscosity, velocity, temperature and pressure.

FIG. 10 depicts a perspective view of another electrodepositionassembly, 1000, of the invention, where the seal and electrolyte portsare configured to aid in formation of substantially laminar electrolyteflow between the substrate and the counter electrode. Assembly 1000includes a manifold with a body, 1005, and a counter electrode, 1010.Substrate 1030 (shown above the manifold) is driven by roller (notdepicted) past the counter electrode as described above, and substrate1030 spans the width of seal 1025 or at least comes in close proximity(for example non-contact sealing with or without overlap of substrateand seal). In this example, seal 1025 has a hexagonal shape (and arectangular cross section). Electrolyte inlet 1015 and electrolyteoutlet 1020 are triangular as depicted, but can be rectangular,circular, oval and the like. The hexagonal shape of seal 1025 aids inproducing a substantially laminar flow by directing electrolyte flowfrom the inlet smoothly, via the angled sides proximate the inlet, toexpand and deflect toward the downstream outlet between the substrateand counter electrode. Laminar flow can also be produced in apparatus1000, for example, by using inlets and/or outlets that flow introduceand/or exit electrolyte from the chamber, for example, as described inrelation to FIG. 9, that is, parallel to the electrode surfaces so thatdiversion from a vertical inlet to a horizontal flow (as depicted inFIG. 10) is avoided.

Another implementation of the sealing is where the edges of thesubstrate, for example a foil substrate, are bent such that it containsthe electrolyte, without touching the counter electrode and causing ashort. In this implementation, the area of the foil that is bent wouldmost likely have to be trimmed and discarded after the fabrication ofthe solar cell stack. These two examples, distinct seals and using aportion of the substrate as a vertical sealing element, are onlyillustrative, non-limiting examples of apparatus components and methodsfor containment of the electrolyte during deposition on the substrate.

Another embodiment is a flow manifold for delivering an electroplatingsolution to the surface of a substrate, the flow manifold including: (i)an electrolyte inlet, the electrolyte inlet upstream of; (ii) a counterelectrode, the counter electrode disposed on a surface of the flowmanifold; and (iii) an electrolyte outlet, the electrolyte outletdownstream of the counter electrode; where the flow manifold isconfigured to supply a continuous flow of the electroplating solutionfrom the electrolyte inlet, between the counter electrode a surface ofthe substrate so that electroplating can occur on the surface of thesubstrate, and then drain via the electrolyte outlet. In one embodiment,the flow manifold is configured to supply electrolyte while engaged witha continuous sheet substrate. In another embodiment, the flow manifoldfurther includes a controller configured to supply the continuous flowof the electroplating solution to the continuous sheet substrate whilethe continuous sheet substrate is moved continuously past and in closeproximity to the counter electrode. In another embodiment, the flowmanifold is configured to produce a substantially laminar flow or aturbulent flow of the electroplating solution between the surface of thesubstrate and the counter electrode. The flow manifold can also includeone or more seals configured to channel the flow of electroplatingsolution in order to maximize contact with the surface of the substrateand minimize the amount of plating solution needed to produce thecontinuous flow of the electroplating solution contacting the substrateduring electrodeposition. The flow manifold can also include one or moreoverflow channels for collecting used electrolyte. The one or more sealscan be configured to form a flow barrier on each of the sides of thesubstrate parallel to direction of electroplating solution flow, and apartial flow barrier on the downstream end of the flow manifold, andoptionally include an upstream seal that forms a flow barrier on theupstream end of the flow manifold. Thus in another embodiment, the oneor more seals are configured to form a chamber or volume between thesurface of the substrate and the flow manifold when the flow manifoldand the substrate are engaged with the one or more seals. In oneembodiment, the flow manifold has a single seal. In a more specificembodiment, the seal is rectangular. Manifold embodiments can alsoinclude pumps and valving configured to recirculate the electrolyte whenflowing but while electrodeposition is not taking place. That is, anembodiment where the apparatus is configured to recirculate theelectrolyte through the manifold until electrodeposition commences andthen the used electrolyte is no longer recirculated through themanifold, but rather diverted for other dispositions, for example,reconstitution or to a waste stream.

Another, more specific, embodiment is an electrodeposition apparatus forfabricating a photovoltaic cell on a continuous substrate, the apparatusincluding: (i) a movement assembly for positioning a substrate betweenabout 2 mm and about 5 mm from a counter electrode duringelectrodeposition; (ii) a flow manifold configured to flow anelectrolyte between the substrate and a counter electrode andcontinuously supply electrolyte between the plating surface of thesubstrate and the counter electrode; (iii) a drive component configuredto move the continuous substrate past the flow manifold and the counterelectrode during electrodeposition without substantially bending thesubstrate; and (iv) one or more seals configured to channel the flow ofelectrolyte in order to maximize contact between only a plating side ofthe continuous substrate and the counter electrode; where the counterelectrode is positioned on, or an integral component of, the flowmanifold and the continuous substrate comprises at least one of anelectrically conductive material and a material having an electricallyconductive coating.

The embodiments described above are not limited to single apparatusworking on, for example, a continuous substrate. One embodiment is anelectrodeposition system including at least two of the flow manifolds asdescribed herein in series that operate on a single continuoussubstrate.

FIG. 11 depicts system, 1100, for electrodepositing multiple layers on asubstrate. In this example, three electrodeposition apparatus, 1110,1120 and 1130, are arranged so that when substrate, 1140, passes fromone apparatus to the next, a first layer is electrodeposited on thesubstrate, then a second layer is deposited on the first layer, and thena third layer is deposited on the second layer. The continuous substratecan move through the apparatus non-stop or stop periodically forelectrodeposition or other processing. In one embodiment, the substratemoves continuously through each of the electrodeposition stations. Inthe example depicted in FIG. 11, each of the first, second and thirdlayers have different compositions and are therefore deposited usingdifferent electrodeposition chemistries. Although depicted as identical,each of the deposition apparatus, 1110, 1120 and 1130, can be of anyconfiguration consistent with the invention as described.Electrodeposition apparatus in accord with embodiments of the inventionallow for many advantages including extreme flexibility when depositingmultiple layers on a single substrate, i.e., they are modular and can beinterchangeable depending upon the desired outcome. For example, notonly can the chemistries vary across different electrodepositionapparatus, but also the individual apparatus can be unique (or not)according to the variables described, such as sealing configuration,shape, contact-type or not, flow parameters, and the like.

Note also in FIG. 11, as indicated by the heavy arrows above and belowthe substrate that there can be pre- and post-processing of thesubstrate's newly deposited layer in between (and after the last)deposition stations. That is, there can be other apparatus positioned inbetween (or prior to the first) electrodeposition apparatus to, forexample, process the substrate prior to entering the first station (forexample preheating, prewetting) or process a newly added film prior toentering a subsequent station, for example, a drying step, a bakingand/or anneal step, and an addition of one or more intervening layers,etc. Metrology can also be performed on the layers in between and/orafter the electrodeposition stations.

Also, since the individual electrodeposition apparatus can be aligned,for example as depicted in FIG. 11, the substrate can be processed inmultiple apparatus without having to be bent, which allows for greaterprocess control and film stability and uniformity. Once the desireddepositions are complete, further post-processing of the substrate, forexample, substrate can then be cut to form individual solar cells whichcan then be tested and sorted based on their performance, followed by abonding operation, and an encapsulation operation to form the solarpanel. The solar cells can be tested for efficiency, open circuitvoltage, short circuit current and the like. The solar cells can bebinned according to, for example, their performance characteristics andappropriately used for fabricating the solar panels. Further details ofserial type operation on a continuous substrate is described in U.S.Provisional Application Ser. No. 61/171,007, which is incorporated byreference herein for all purposes.

As one of ordinary skill in the art would appreciate, theelectrodeposition apparatus in accord with embodiments of the inventionmay also include a controller system for managing the differentcomponents of the system. By way of examples, the controller may beconfigured or programmed to select the potential difference that isapplied between the substrate and the electrode, control theelectrolytic flow rate and fluid management, control the movementmechanism, and the like. Any suitable hardware and/or software may beutilized to implement the controller system. For example, the controllersystem may include one or more microcontrollers and microprocessors suchas programmable devices (for example, complex programmable logic devices(CPLD's) and field programmable gate arrays (FPGA's) and unprogrammabledevices such as gate array application specific integrated circuits(ASIC's) or general-purpose microprocessors and/or memory configured tostore data, program instructions for the general-purpose processingoperations and/or the inventive methods described herein.

Another embodiment is an electrodeposition method including: (i) flowingan electrolyte between a substrate and a counter electrode using a flowmanifold that supplies a continuous supply of electrolyte to thesubstrate while the plating surface of the substrate is in closeproximity to the counter electrode; and (ii) applying a platingpotential between the substrate and the counter electrode; where thecounter electrode is configured to substantially span at least onedimension of the substrate and is positioned on, or an integralcomponent of, the flow manifold.

FIG. 12 depicts a process flow, 1200, for this method embodiment. First,an electrolyte flow is established between a substrate and a counterelectrode, where the substrate and counter electrode are in closeproximity (as described above in relation to apparatus of the invention)using, for example, a flow manifold as described above, see 1210. Then aplating potential is between the substrate and counter electrode so thatelectrodeposition of a species from the electrolyte to the substrate isachieved, see 1220. Then the process flow ends. In one embodiment, themethod further includes moving the substrate continuously past thecounter electrode during electrodeposition, where the substrate includesa continuous sheet, the continuous sheet including at least one of anelectrically conductive material and a material having an electricallyconductive coating.

In another embodiment, the method further includes: (iii)electrodepositing material onto the substrate while the substrate isstationary; (iv) repositioning the substrate so that an area withoutelectrodeposited material is positioned for electrodeposition; and (v)electrodepositing material onto the area; where the substrate is acontinuous sheet including at least one of an electrically conductivematerial and a material having an electrically conductive coating. Inone embodiment, close proximity means the counter electrode and thesubstrate are positioned between about 2 mm and about 25 mm apart duringelectrodeposition, in another embodiment between about 2 mm and about 10mm apart during electrodeposition, and in another embodiment betweenabout 2 mm and about 5 mm apart during electrodeposition. In yet anotherembodiment, close proximity means the counter electrode and thesubstrate are positioned between about 1 mm and 2 mm apart. In anotherembodiment, the counter electrode and the substrate are between about0.1 mm and about 2 mm apart. In one embodiment, flowing an electrolytebetween the substrate and the counter electrode includes producing asubstantially laminar flow or a turbulent flow of the electrolytebetween the substrate and the counter electrode. In one embodiment theflow is substantially laminar. In another embodiment, the method furtherincludes employing one or more seals configured to channel the flow ofelectrolyte in order to maximize contact with the substrate and minimizethe amount of electrolyte needed to produce the continuous supply ofelectrolyte contacting the substrate during electrodeposition.

In a more specific embodiment, the one or more seals are configured toform a chamber (or volume) between the substrate and the flow manifoldwhen the flow manifold and the substrate are engaged with the one ormore seals; the flow manifold further including an electrolyte inletconfigured to supply electrolyte to the chamber and an electrolyteoutlet configured to drain used electrolyte from the chamber duringelectrodeposition. In another embodiment, the one or more seals areconfigured to form a flow barrier on each of the sides of the substrateparallel to direction of electrolyte flow, and a partial flow barrier onthe downstream end of the flow manifold, and optionally an upstream sealthat forms a flow barrier on the upstream end of the flow manifold,where the flow manifold further includes an electrolyte inlet, theelectrolyte inlet located downstream of the upstream seal. The seals canbe attached to at least one of the flow manifold and the counterelectrode. In the chamber or volume embodiments, the one or more sealsinclude a single rectangular seal or a seal of a shape as described inrelation to the apparatus above.

Certain embodiments of the present invention have several associatedadvantages. One advantage can be lower maintenance than conventionalelectrodeposition apparatus. For example, in embodiments employing acontinuous substrate, only one surface of the substrate comes in contactwith the electrolyte, and this arrangement significantly mitigates thechemical compatibility issues for the parts and also reduces the cost ofthe equipment significantly. Maintenance of this equipment is easy sinceonly a relatively small number of parts of the equipment are exposed toharsh chemicals.

Another advantage can be lower chemical consumption than in conventionalsystems. In one implementation, the chemical consumption is reducedsignificantly since only a thin film of liquid is used for depositionand only one surface of the substrate, along with the counter electrode,is in contact with the electroplating solution.

Another advantage can be deposition uniformity. Since a thin film ofelectrolyte is constantly flowing past the electrodes, a significantlybetter chemical uniformity can be achieved by replenishing the chemicalsdepleted during the deposition process. In one implementation, asubstantially parallel plate configuration can be achieved, for exampleby making the manifold electrode larger than the continuous substrate,for example as depicted in FIG. 5B. This is only one possiblearrangement to achieve this result. Many other variations of thisimplementation can achieve a parallel plate configuration. In theillustrated example, the substrate temperature, potential, and flatnesscan be controlled very precisely since the substrate is in contact withthe roller. Also, the temperature of the electrolyte can be controlledvery precisely since it is a thin film of flowing electrolyte and heatloss due to dissipation at the edges represents only a very smallpercentage of total liquid volume.

Yet another advantage over conventional apparatus and methods can bemodularity and interchangeability. Certain implementations lendthemselves very well to modularity and interchangeability. The samemanifold and infrastructure can be used for multiple depositions sincethe chemical compatibility of the parts is not an issue because only theelectrodes are wetted. The manifolds in this implementation can be sizedfor the fastest deposition in a multiple deposition line and for longerdepositions multiple manifolds can be used to achieve the targetedthickness. Other advantages with respect to modularity are describedabove in relation to FIG. 11.

Certain embodiments of the electrodeposition apparatus and methodsdescribed herein, for example on continuous substrates, overcome most ofthe challenges associated with conventional methods of electrochemicaldeposition, significantly reducing the cost of the equipment, reducingthe chemical consumption, enhancing the maintainability, depositionuniformity, and it is modularity and interchangeability.

Although the foregoing invention has been described in some detail forpurposes of clarity of understanding, it will be apparent that certainchanges and modifications may be practiced within the scope of theappended claims. Therefore, the present embodiments are to be consideredas illustrative and not restrictive and the invention is not to belimited to the details given herein, but may be modified within thescope and equivalents of the appended claims.

1. An electrodeposition apparatus, comprising: (i) a movement assemblyfor positioning a substrate in close proximity to a counter electrodeduring electrodeposition; and (ii) a flow manifold configured to flow anelectrolyte between the substrate and a counter electrode andcontinuously supply electrolyte between the plating surface of thesubstrate and the counter electrode; wherein the counter electrode ispositioned on, or an integral component of, the flow manifold.
 2. Theapparatus of claim 1, wherein the movement assembly is configured tomove a continuous sheet type substrate, said continuous sheet typesubstrate comprising at least one of an electrically conductive materialand a material having an electrically conductive coating.
 3. Theapparatus of claim 2, wherein the movement assembly comprises a drivecomponent configured to move the continuous sheet type substrate pastthe flow manifold and counter electrode during electrodeposition withoutsubstantially bending the substrate.
 4. The apparatus of claim 3,wherein the counter electrode is configured to substantially span thewidth of the continuous sheet type substrate as the continuous sheettype substrate passes by the counter electrode during electrodeposition.5. The apparatus of claim 4, wherein the counter electrode comprises asubstantially planar surface that is positioned substantially parallelto the surface of the substrate during electrodeposition.
 6. Theapparatus of claim 5, wherein the counter electrode and the substrateare between about 2 mm and about 10 mm apart during electrodeposition.7. The apparatus of claim 6, wherein the flow manifold is configured toproduce a substantially laminar flow or a turbulent flow of theelectrolyte between the substrate and the counter electrode.
 8. Theapparatus of claim 7, further comprising one or more seals, said sealsconfigured to channel the flow of electrolyte in order to maximizecontact with the substrate and minimize the amount of electrolyte neededto produce the continuous supply of electrolyte contacting the substrateduring electrodeposition.
 9. The apparatus of claim 8, furthercomprising one or more overflow channels for collecting usedelectrolyte.
 10. The apparatus of claim 8, wherein the one or more sealsare configured to form a chamber between the substrate and the flowmanifold when the flow manifold and the substrate are engaged with, orin close proximity to, said one or more seals; said flow manifoldfurther comprising an electrolyte inlet and an electrolyte outlet, eachcontained within the chamber during electrodeposition.
 11. The apparatusof claim 10, wherein the one or more seals comprise a perimeter-typeseal.
 12. An electrodeposition method comprising: (i) flowing anelectrolyte between a substrate and a counter electrode using a flowmanifold that supplies a continuous supply of electrolyte to thesubstrate while the plating surface of said substrate is in closeproximity to the counter electrode; and (ii) applying a platingpotential between the substrate and the counter electrode; wherein thecounter electrode is configured to substantially span at least onedimension of the substrate and is positioned on, or an integralcomponent of, the flow manifold.
 13. The method of claim 12, furthercomprising moving the substrate continuously past the counter electrodeduring electrodeposition, wherein the substrate comprises a continuoussheet, said continuous sheet comprising at least one of an electricallyconductive material and a material having an electrically conductivecoating.
 14. The method of claim 13, wherein the counter electrode andthe substrate are positioned between about 2 mm and about 10 mm apartduring electrodeposition.
 15. The method of claim 14, wherein flowing anelectrolyte between the substrate and the counter electrode comprisesproducing a substantially laminar flow or a turbulent flow of theelectrolyte between the substrate and the counter electrode.
 16. Themethod of claim 15, further comprising employing one or more seals, saidseals configured to channel the flow of electrolyte in order to maximizecontact with the substrate and minimize the amount of electrolyte neededto produce the continuous supply of electrolyte contacting the substrateduring electrodeposition.
 17. The method of claim 16, wherein the one ormore seals are configured to form a chamber between the substrate andthe flow manifold when the flow manifold and the substrate are engagedwith said one or more seals; said flow manifold further comprising anelectrolyte inlet configured to supply electrolyte to the chamber and anelectrolyte outlet configured to drain used electrolyte from the chamberduring electrodeposition.
 18. The method of claim 17, wherein the one ormore seals comprise a perimeter-type seal.
 19. A flow manifold fordelivering an electroplating solution to the surface of a substrate,said flow manifold comprising: (i) an electrolyte inlet, the electrolyteinlet upstream of; (ii) a counter electrode, the counter electrodedisposed on a surface of the flow manifold; and (iii) an electrolyteoutlet, the electrolyte outlet downstream of the counter electrode;wherein the flow manifold is configured to supply a continuous flow ofthe electroplating solution from the electrolyte inlet, between thecounter electrode a surface of the substrate so that electroplating canoccur on the surface of the substrate, and then drain via theelectrolyte outlet.
 20. The flow manifold of claim 19, configured toproduce a substantially laminar flow or a turbulent flow of theelectroplating solution between the surface of the substrate and thecounter electrode.
 21. The flow manifold of claim 20, further comprisingone or more seals, said seals configured to channel the flow ofelectroplating solution in order to maximize contact with the surface ofthe substrate and minimize the amount of plating solution needed toproduce the continuous flow of the electroplating solution contactingthe substrate during electrodeposition.
 22. The flow manifold of claim21, further comprising one or more overflow channels for collecting usedelectrolyte.
 23. The flow manifold of claim 21, wherein the one or moreseals are configured to form a chamber between the surface of thesubstrate and the flow manifold when the flow manifold and the substrateare engaged with said one or more seals.
 24. The flow manifold of claim23, wherein the one or more seals comprise a perimeter-type seal.